1. Field of the Invention
This invention relates to a technique for accessing a recording medium that has a track structure of lands and grooves and is divided into an identification area and a user information area, and more particularly to an information recording and reproducing method and apparatus wherein the track and/or the areas is identified by an information on the identification area and the information record and reproduction is performed depending upon the identified result.
2. Description of the Prior Art
Recently, there have been developed and prevalent various types of recording media to record as much information as possible. For example, in a digital versatile disc(DVD), a width of track and a distance between tracks, that is, a track pitch, etc. are reduced compared with the existing compact disc(CD) so as to record more information.
In a recording medium such as an optical disc, a track is defined by the land and groove pattern to perform an accurate information record and reproduction including an effective tracking. The optical disc having such land and groove tracks can be classified into an optical disc in which an information is recorded only on the groove track and an optical disc in which an information is recorded on both the land track and the groove track. Typically, the latter optical disc has a two spiral track structure in which the land and groove tracks are formed in parallel in the spiral pattern from the innermost circumference to the outermost circumference. In an optical disc having such a two spiral track structure, typically, the record and reproduction (i.e., an excess operation) is performed for any one of the land and groove tracks and, thereafter, performed for the remainder track. Alternatively, there exist an optical disc having an one spiral track structure in which the land and groove tracks are alternately arranged every rotation.
A track of the recording medium such as optical disc is divided into a certain size of unit regions, hereinafter referred to as "sectors", to record an information in a certain size of block unit. The sector consists of a preceding ID area and a user information area following the ID area. The user information area is called "recording area" because an information desired by a user is recorded in this area. The ID area is recorded with an ID code indicating a physical position of the track.
FIG. 1 shows an optical disc in which an ID area and a user information area are formed in a different pattern and the user information area is defined by land and groove tracks. An example of such an optical disc is disclosed in Japanese laid-open patent gazette no. Pyung 9-221821. In the disc as shown in FIG. 1, land tracks 1 and groove tracks 2 are alternately arranged in the diameter direction. All the land and groove tracks 1 and 2 are used as the user information area that permits a user to record a desired information. Further, the land and groove tracks 1 and 2 are alternately arranged in the circumference direction of the disc along with a certain length of embossed pit stream 3 and 4. The certain length of embossed pit stream 3 and 4 divides the land and groove tracks 1 and 2 in a number of sectors and indicates the physical position of the sectors. Accordingly, a region occupied by the embossed pit stream 3 and 4 is referred to as "ID area". The embossed pit stream 3 and 4 consist of the first pit stream 3 and the second pit stream 4. The first pit stream 3 is defined on the upper side with respect to the center line of the land track 1, and the second pit stream 4 is defined on the lower side with respect to the center line of the land track 1. Since the first pit stream 3 includes an identification code indicating the physical position of the land track 1, a region occupied by the first pit stream 3 is referred to as a land ID area. Likewise, since the second pit stream 4 includes an ID code indicating the physical position of the groove track 2, a region occupied by the second pit stream 4 is referred to as a groove ID area. Each side of the land and groove tracks 1 and 2 may be formed in a linear line as shown in FIG. 1, or may be formed in a wobbled pattern having a certain period so as to indicate a rotation speed of a disc and a tracking of a light beam. In other words, a wobbling signal may be preformatted at each side of the land and groove tracks 1 and 2. This wobbling signal may include a carrier signal in which a specified information such as an address indicating the physical position of a disc is frequency modulated.
In order to access an optical disc having tracks formed in the land and groove pattern, a light beam must trace the center of the land and groove tracks accurately. To this end, a light beam must be controlled differently depending upon the land or groove track. Accordingly, a tracking servo controlling a tracking of a light beam must quickly and accurately determine whether a track at which a light beam is positioned is the land track or the groove track.
Likewise, in order to accurately access an optical disc in which the user area and the ID area are defined in a different pattern, an ID code preformatted on the ID area must be accurately detected in a method different from an information recorded in the user area. To this end, a tracking servo must control a tracking of a light beam differently depending upon the user area and the ID area. Accordingly, the tracking servo must quickly and accurately identify the ID area and the user area.